ETO Project Commitments For Distribution Items

My current client is a construction company who acts also as a distributor (no manufacturing).  We are utilizing Job Cost for their projects, and as part of that we will be purchasing materials for the project.

In using ETO, we have been able to create the ETO Project and subtasks (we are doing one subtask per distribution item we are purchasing).  We can create a PO from that subtask, and it shows fine as Related Orders in the P31P204.

The problem is when we do a receipt.  When we receive this product, we want it to commit to the project to keep it from being selected for any other Sales Order other than the one we would create through ETO.  I can't get the inventory to show up in the F410211 against our project.  I have read all the support documents for ETO commitments, but they all seem to imply that we need a Parts List, but we don't have Parts Lists because we don't do manufacturing.  What am I missing?  We need to be able to segregate project